1. Field of the Invention
The present invention relates to a device for detecting the opening of a throttle valve which adjusts the intake volume for an engine. More particularly, the present invention is concerned with a throttle valve opening detecting device capable of correcting an individual difference between individual throttle valve products to effect a highly accurate detection of throttle valve opening.
2. Description of the Related Art
FIG. 8 shows schematically the appearance of a conventional device for detecting the opening of a throttle valve. In this conventional device, mounting holes of an opening sensor 91 for a throttle body are formed as long holes to permit adjustment of the mounting angle. In the interior of the opening sensor 91 are mounted a substrate 80 and a slider 83 connected to the throttle valve. A conductor pattern 81 and a resistor pattern 82 are formed on the substrate 80 in such a double arc shape as shown in FIG. 6. The substrate 80 is fixed to an outer frame of the opening sensor 91, both ends of the resistor pattern 82 are connected to terminals 84 and 86, and the conductor pattern 81 is connected to a terminal 85. On the other hand, both ends of the slider 83 are in contact at both ends thereof with the conductor pattern 81 and the resistor pattern 82, and the contact positions thereof shift with movement of the throttle valve. Since a supply voltage V.sub.SS is applied to the terminals 84 and 86, a voltage V.sub.A obtained by dividing the supply voltage V.sub.SS by the resistor pattern 82 and the slider 83 appears at the terminal 85 through the conductor pattern 81. Since the voltage V.sub.A differs depending on the opening of the throttle valve, it can be used as a signal for detecting the opening of the throttle valve.
The throttle body and the opening sensor 91 each involve an individual difference based on, for example, machining accuracy within the tolerance of their components. Therefore, the characteristic of the voltage V.sub.A for the opening of the throttle valve does not strictly agree with that of another throttle valve product. Therefore, an ideal product constituted by only ideally machined components is provided, then the voltage V.sub.A is measured at a throttle opening which affords an intake volume (2 m.sup.3 /h at a bore of 35 mm.phi. and a negative pressure of 60 kPa, for example) corresponding to an idling condition. The throttle opening will hereinafter be referred to as "fully closed" for convenience' sake. The voltage thus measured is recorded as V.sub.0. Then, the throttle opening is adjusted so that the same intake volume is obtained with an actual product, and the mounting angle of the opening sensor 91 for the throttle body is adjusted so that the voltage V.sub.A becomes V.sub.0 in this condition.
If this adjustment is made, the detected voltage V.sub.A in idling becomes V.sub.0 for all the products irrespective of an individual difference among the products. In actual operation, therefore, the value (V.sub.A -V.sub.0) obtained by subtracting V.sub.0 from the detected voltage V.sub.A is used as a detection signal T.sub.A. The detection signal T.sub.A can be converted to the opening of the throttle valve by multiplication using an appropriate coefficient. The throttle valve opening thus calculated is employable in calculating the fuel injection volume or in various controls, including control of the speed changing operation of an automatic transmission. Examples of such a throttle valve opening detecting device are disclosed in Japanese Utility Model Laid Open No. 62-81004 (with an idling switch) and Japanese Patent Laid Open No. 3-281947 (without an idling switch).
However, the following problems are encountered in the conventional throttle valve opening detecting device described above. In the conventional device, it is only in the fully closed state of the throttle valve that an individual difference between products is adjusted. In actual products, however, such an individual difference exerts an influence not only on the fully closed state but also on an open condition of the throttle valve. Besides, the degree of the influence is not constant continuously from the fully closed state. This is because there is an individual difference also with respect to the degree of change in the intake volume for a change in the throttle valve opening and output characteristics of the opening sensor 91. Consequently, as indicated with broken lines in the graph of FIG. 7, even if adjustment is made so that an error does not exceed .+-.5% or so in the fully closed state of the throttle valve, it is unavoidable for the error to increase with an increase of the throttle valve opening. In the state of a large throttle valve opening, it is possible that various controls will become rough.